CPS sum overflows the stack in Debug, and in Release only the second function does

Hello all,

I am working through continuation-passing style as an exercise, using a small sensor tool for my data work. loadReadings generates a list and stands in for a CSV loader I have not written yet. Then I total the values in two ways. Both are written so the recursive call is the last thing that happens, as I understand it.

let rec sumK (xs: int list) (k: int -> int) =
    match xs with
    | [] -> k 0
    | x :: rest -> sumK rest (fun s -> k (s + x))

let rec sumCheckedK (xs: Reading list) (k: int -> int) =
    match xs with
    | [] -> k 0
    | r :: rest ->
        try
            if r.Value < 0 then
                failwithf "faulty reading from %s" r.Sensor
            sumCheckedK rest (fun s -> k (s + r.Value))
        with ex ->
            log ex.Message
            sumCheckedK rest k

In main I call sumK values id, then sumCheckedK readings id, with the default 1,000,000 readings (every 250000th is a faulty -1).

• dotnet run (Debug): dies almost immediately with Stack overflow. and a huge repeating trace, before any total.
• dotnet run -c Release: the sumK total prints correctly, then Stack overflow. again, with a repeating frame mentioning sumCheckedK.
• With -- 10000 both builds work.

My first suspicion was the list construction, but the Release run shows that is fine. Then I wondered whether the JIT gives up on deeply nested closures. I do not set anything special in the fsproj (net8.0, .NET 8 SDK, Rider on an M-series Mac).

Is this one problem or two? I would rather understand it than just enlarge the thread stack.